FIG. 1 is an illustration of the principle of operation of a zirconia oxygen sensor, wherein a zirconia ceramic element 1 that is stablized with yttria (Y.sub.2 O.sub.3) or calcia (CaO) and is heated to high temperatures to form a solid electrolyte with only mobile oxygen ions. Catalytic electrodes 2 of platinum are formed on both sides of the stabilized zirconia element 1 and a voltage V is applied across the electrodes 2. In contact with one of the electrodes 2 which is biased to the lower potential, oxygen is converted into O.sup.2 ions. Current flows through the stabilized zirconia element 1 and the oxygen content can be determined from the current level.
FIG. 2 is an illustration of a limited current type oxygen sensor using the stabilized zirconia element 1. As shown in FIG. 2, a minute diffusion orifice 4 is provided with a cover 3. Dry-gas-based oxygen content excluding water vapor is normally required to determine oxygen content and this makes it necessary to supply gas being examined without water vapor content separately for correction purposes. The above methods are disadvantageous in that they require complicated arrangements and make the measuring process tedious and complicated.